feat: complete Syndarix rebranding from PragmaStack

- Update PROJECT_NAME to Syndarix in backend config
- Update all frontend components with Syndarix branding
- Replace all GitHub URLs with Gitea Syndarix repo URLs
- Update metadata, headers, footers with new branding
- Update tests to match new URLs
- Update E2E tests for new repo references
- Preserve "Built on PragmaStack" attribution in docs

Closes #13

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/tests/components/layout/Footer.test.tsx

@@ -20,7 +20,7 @@ describe('Footer', () => {
 
       const currentYear = new Date().getFullYear();
       expect(
-        screen.getByText(`© ${currentYear} PragmaStack. All rights reserved.`)
+        screen.getByText(`© ${currentYear} Syndarix. All rights reserved.`)
       ).toBeInTheDocument();
     });